The present invention relates to nut locks, and more particularly to nut locks that includes a locking coil.
When nut and bolt assemblies require high strength and high resistance to loosening, prevailing torque locknuts are not generally used. More positive mechanical locking means are preferred. There are a number of methods used including adhesives, serrated hex-flange nuts, jam nuts, cotter pins, lock wiring, welding, locking pins or locking rings with keyways, and various added mechanical components that capture nuts or bolt heads and lock them in position by connecting to adjacent structure. In cases where adjacent structure is used, constraints must be added to both nut and bolt head to prevent relative rotation. The noted locking means all have limitations.
Adhesives require proper surface preparation and may not be appropriate where service requires removal.
Serrated hex-flange nuts are effective for joints with materials having hardness less than 40 RC. For nut and bolt assemblies, both the bolt and the nut must use serrated flanges. The serrations can damage painted and coated surfaces and lead to corrosion.
A jam nut is a second threaded nut, usually thinner, which is tightened against the main load-bearing nut. The use of jam nuts is controversial and is not recommended by the Industrial Fastener Institute, because load-sharing between the two nuts is difficult to control and can lead to loosening or failure of the jam nut threads.
Special jam nut designs marketed under the Hard Lock trademark include a threaded main nut that has an eccentric convex conical backside that mates with a threaded jam nut that has a centered concave conical mating surface. While this design is claimed to function effectively, it is relatively complex and requires training to use properly. A significant limitation is that it must be integral with the nuts so it cannot be used with standard nuts.
Cotter pins and lock wires can positively retain nuts, but they do not maintain bolt tension.
Nuts and bolts can be welded together or to adjoining structure. This can be effective, but must be done only by skilled and trained operators and only where a permanent joint is acceptable.
Specialized fasteners sold under the Huck Lockbolt, Truelock Bolt, and Axilok Nuts use locking rings and keyways to mechanically lock nuts and bolts. These are complex mechanical systems that cannot be used with standard nuts and bolts.
Other specialized mechanical locking systems are used such as the Nordlock ramped washer system and the Stage 8 system. Both of these anchor either the bolt head or the nut to adjacent structure and prevent rotation of the anchored component. Two sets must be used if relative rotation between the nut and bolt is required. This adds expense and complexity. The Nordlock system requires a limit to the hardness of the adjacent structure so that the serrated washer can embed and grip to prevent rotation. This can damage softer materials, as well as painted or coated surfaces. The Stage 8 system requires sets of various hardware components to prevent the counterclockwise rotation of bolt heads or nuts by anchoring them to adjacent structure.